"Thirty years ago, the two sides of the river were virtually identical," says a Chinese businessman who frequently travels to North Korea. "But now, it seems they couldn't be more different."

North Korea's attempt to create a communist Utopia is ruining its economy, while China's abandonment of Marx in favor of free markets is triggering high-speed growth.

International aid groups and Chinese who have visited the reclusive North say a famine is slowly spreading out across the country.

The North's tight controls over its 23 million residents and its borders are preventing a flood of refugees into China, says a South Korean official. "We believe North Korea's border guards have orders to shoot anyone attempting to flee the country."

Ever-present patrols on the North Korean riverfront focus their gaze on their compatriots rather than on any would-be foreign intruders.

"Guards carrying machine guns are posted ... throughout the North," says the Chinese businessman in Dandong. "The sense of repression and deprivation is so great that even Chinese officials have complained about the human rights situation in North Korea," he adds.

Although the North is one of the poorest countries in Asia, it maintains a 1 million-strong Army.

A cease-fire halted the 1950-1953 Korean War, which pitted the North and China against South Korea and the US more than 40 years ago. But North Korea's state-run press says the military buildup is needed to protect from "US war maniacs," who could reignite the conflict.

This area of the Yalu gained the limelight near the war's beginning, when American jet fighters strafed the original bridge that crossed the river. A new structure, parallel to the original, was built after the war.

But while the Stalinist North still seems to be in a state of military alert, Chinese entrepreneurs have transformed Dandong's war sites into tourist attractions. For 10 yuan ($1.25), thrill-seekers can cross the restored, bombed-out shell of the original Yalu bridge.

Near the twisted girders at the bridge's end, they can rent Chinese or American Army uniforms, along with mock machine guns and hand grenades, to have their photos taken. The spirit of freewheeling capitalism has even permeated China's border guards, who operate speedboats that take tourists to within 50 feet of the North Korean shore.

During the Korean War, Chinese troops fought alongside their North Korean comrades to further the global march of socialism. But the relationship between the onetime allies is showing signs of tension as China embarks on the road toward capitalism, say many Chinese here.

"Lately, the North Koreans have begun throwing stones at Chinese tourists who try to take pictures of life on the other side of the river," says a Chinese tour guide in Dandong. "The North Koreans can see the growing gap between their poverty and our wealth, and they are afraid the photos could be used to humiliate them," he adds.

Although China still considers the North a strategic ally, it is quietly pressing leaders in the North Korean capital, Pyongyang, to move forward in peace talks with the US and South Korea.

And patience seems to be wearing thin among some Chinese leaders with North Korea's aggressive military and failing economy. "A delegation of Chinese veterans of the Korean War, including high-ranking [Communist] Party officials, recently rejected an invitation to visit Pyongyang," says a Chinese government worker in Beijing.

Chinese officials blamed the North for recent border clashes with the South and for causing a famine through economic mismanagement, he adds.

The North felt betrayed after China forged diplomatic ties with Seoul and was infuriated when a top North Korean official was permitted to defect while passing through Beijing earlier this year.

Despite the private gripes between the onetime communist allies, China and North Korea have maintained a public stance of friendship.

The North's official news agency reported that China donated 80,000 tons of food to the North last week, and aid groups say Beijing has saved countless lives by throwing across a grain lifeline.

"The people of North Korea should not be made to suffer for the political and economic mistakes of their leaders," says a Chinese official here.

And in a statement that eerily echoes US policy toward China, he adds: "Beijing believes that only through engagement and gradually coaxing North Korea onto the world stage can it be made a more responsible player."

Each dawn, a convoy of Chinese trucks, many loaded with corn or rice, slowly crosses the Yalu bridge. Yet few North Koreans obtain the rare government permits needed to cross the bridge to China.

"Most of the North Koreans who cross the Yalu attempt the journey under the cover of night," says the Chinese businessman. "Yet with so many guards on the North Korean shore ... few manage to make it to the riches and freedom that China must represent to them," he adds.